Many machines and equipment include compressed air systems that provide compressed air to perform various functions. Such compressed air systems may include an air compressor that is driven by an engine of the machine, an inlet valve that regulates airflow to an inlet of the air compressor, and a reservoir that stores the compressed air generated by the air compressor. For example, drill machines (such as track drill machines), surface rock drills, and rotary drill machines may supply compressed air down a drill rod to flush dust out of a hole as the hole is being drilled by the drill rod. Such machines may also rely on compressed air to perform such functions, such as driving the flow of lubricating oil through the air compressor, and intermittently cleaning filters of a dust collector which collect the dust of the material that is flushed out of the hole. To perform such functions, compressed air may be directed to various downstream sites (e.g., the drill rod, the dust collector filter, etc.) from the reservoir.
The pressure of the compressed air in the reservoir may be carefully regulated to both support the downstream functions of the machine that rely on compressed air, and to prevent over pressurization of the reservoir. For instance, even when the inlet valve to the air compressor is closed, the reservoir may be continuously charged with compressed air due to leakage of air through one or more orifices of the inlet valve, possibly allowing excess pressure to build up in the reservoir. To avoid over pressurizing the reservoir, the compressed air system may include a pressure release valve, or a running blow down valve, that opens to allow release of the compressed air in the reservoir to the atmosphere when the machine is running. The outflow of the running blow down valve may be regulated by manual adjustment of the valve orifice size. In addition, a separate blow down valve of a fixed orifice size may allow the compressed air in the reservoir to escape to the atmosphere when the machine is turned off.
Tank pressure release through the running blow down valve may be relatively slow as it relies on outflow of compressed air through the fixed orifice of the valve to depressurize the reservoir to a desired level. Furthermore, during drilling, the running blow down valve may be open and allow compressed air, which could otherwise more effectively be delivered to the drill rod, to leak to the atmosphere. As a result, the efficiency of the compressed air system may be reduced, and power burdens on the engine may be needlessly increased. Moreover, the running blow down valve and the blow down valve may be pneumatically controlled through pneumatic actuators, such as pneumatic cylinders. In some circumstances, pneumatic control of the running blow down valve and the blow down valve may be inefficient, unreliable, and unstable.
U.S. Pat. No. 5,265,547 discloses an air drill that uses air to meter seeds to planter units. The air drill includes a butterfly valve for selectively diverting the seeds to one or both of two different planter units. A solenoid actuator is used to control a position of the butterfly valve. However, the patent does not mention strategies for regulating the pressure of compressed air stored in a compressed air reservoir. There is a need for improved control systems for regulating the pressure of compressed air reservoirs in machines having compressed air systems.